A similar device is known from FR 2,557,933. It is used particularly in the context of an external fixator. It comprises a rectangular internal rod and a hollow tube surrounding the same, which are thus movable in one another in a torsion-resistant manner. The adjustment is to be made by means of a nut and an adjusting screw, disposed at the free end of the hollow tube. At the two ends of the device, a clamping member is or will be attached that is connected to the bone fragments by means of rods or pins. A clamping member is attached to the hollow tube by means of a bracket that is thus resistant to torsion in relation to the axis of the rectangular tube. At the free end of the interior shaft, an additional clamping member is attached through a longitudinal screw that can be screwed into internal rod, which is thus freely rotatable in relation to the axis of the rectangular internal rod. Non-metallic materials are used as the material for disposable use. After fixation of two facing bone fragments with two clamping members, it is possible, by means of actuation of the adjustment device, i.e., the nut and adjusting screw, to extend the distance between the attachment points of the fixator to the bone, i.e., to extend the length of the bone overall.
Another such device is known from U.S. Pat. No. 5,454,810. This publication targets the problem of the use of a rotationally-symmetrical inner rod and outer tube in relation to rotatory stability. In U.S. Pat. No. 5,454,810, a round outer tube with a bore of continuous square cross-section is used so that an internal rod with a square cross-section can be used in the outer tube. The outer tube is composed of two aluminum halves while the inner rod is made of steel. To avoid jamming, the prior art uses polymeric material strips in the bore.
The free end of the inner rod ends in a larger diameter part projecting out from the outer tube. This end serves to fix the one clamping member. The other end of the inner rod in the telescoping version of the device according to U.S. Pat. No. 5,454,810, shown with members in FIG. 8 therein, connects with a slide that is axially movable by means of a screw thread.
Other such devices are shown in U.S. Pat. Nos. 5,275,599 and 4,475,546.
These devices present the disadvantage that they are difficult to adjust because both publications refer to the operating surgeon effecting adjustments. The fixation knobs at the free ends, in contrast to this, can also be actuated unintentionally by the patients both in the hospital and under outpatient treatment and can thus be misadjusted.
One disadvantage of existing devices of this type therefore lies particularly in the fact that they are not simple to use. They should, advantageously, be changeable to a defined extent by the user as well, e.g., a patient should be able to extend said distance, i.e., said bone length, him/herself, in the simplest manner. At the same time, the device should be protected against unintentional actuation.